#BBCtrending: 10 theories about the Brooklyn Bridge flags

When New Yorkers woke on Tuesday morning they were greeted by the sight of two large white flags in place of the stars and stripes that normally fly over the landmark Brooklyn Bridge.

The news quickly became a national story, with more than 30,000 bridge-related posts on Twitter speculating about the meaning of the act and the parties responsible.

Much of the chatter was humorous, but one joke didn't end up that way. The Twitter account @BicycleLobby sent out: "Earlier today we hoisted two white flags to signal our complete surrender of the Brooklyn Bridge bicycle path to pedestrians."

The Associated Press and the New York Daily News picked up the story and reported it as a legitimate claim of responsibility, despite the fact that the tweeter's bio said it was a parody account. As the message received widespread coverage, @BicycleLobby tweeted: "If you believe we're for real, we have a bridge in Brooklyn we'd like to sell you."

On Wednesday morning, speculation centred on the Instagram user Last Suspect, who according to the New York website Gothamist, posted images of bleached white flags and photos taken underneath the Brooklyn Bridge, along with now-deleted comments insinuating involvement in the plot.

Finger of blame

(according to Twitter)

1) Hipsters

2) Anti-hipsters

3) Bicyclists

4) Gentrifiers

5) Jasper Johns

6) Triumphant Brooklynites

7) Humble Manhattanites

8) Surrendering French

9) Starbucks

10) Aliens? Yes, definitely aliens

Much of the theorising has focused on the white flag as a symbol of surrender. The words "Brooklyn" and "surrender" have been used together several thousand times on Twitter since the story broke.

But who was surrendering to whom?

It could have something to do with the oh-so-cool reputation of Brooklyn neighbourhoods. Among the possible theories were:

And then there were those who decried the extensive media coverage of the flag incident when there were more serious matters going on in the world.

"Death and destruction in Gaza, Russia's invading Ukraine, but thank god the media is all over a couple of white flags on the Brooklyn Bridge," tweeted Eric Fastner.

New York police agree that this isn't a laughing matter and say they are conducting a full investigation.

Seven years ago, Boston was paralysed by an ill-advised viral-marketing campaign for a television show after police and city residents mistook "light-up" placards placed in public spaces for improvised explosive devices.

Although the white-flag incident hasn't prompted the same level of panic, 13 years after the 9/11 attacks on Manhattan, the response shows some New York nerves are still a little raw.

"Could this be a shot across the bow, letting the American public know just how vulnerable we still are?" writes Jennifer Van Laar of IJReview.

"This time it was a flag," blared the New York Daily News headline, "next time it could be a bomb."